DX:HR, purely played as a stealth game and ignoring the action elements, is better than Thief 3. Enemy behaviour is more sophisticated (like they can actually turn their heads and look around) and the cover system is superbly integrated with the stealth system. Dishonored is too; is has bigger levels, better AI, and more opportunity for improvisation. Mark of the Ninja isn't "AAA", and it's 2D, but despite that has the most complex stealth mechanics of probably any game.
A game on the level of Thief 3 would be a significant step backwards from what we have now.